1. Field of the Disclosure
The present invention relates generally to flame retardant electronic circuitry packaging. More specifically, the methods and compositions of the present invention are directed to the use of flexible, aqueous-processible, photoimagable coverlay compositions having little, if any, halogen (compared to conventional flame retardant coverlays), due at least in part to the use of a phosphorus based chemistry.
2. Description of Related Art
Photosensitive coverlay compositions can be generally referred to as “solder masks.” These compositions are discussed broadly in U.S. Pat. No. 5,536,620 to Dueber et al. Flame retardant properties (i.e., flame retardancy) can be important in certain applications. Typically, halogenated materials have been used to make these materials flame retardant. However recently, increasing environmental concerns have required manufactures to make halogen-free flame retardant coverlay materials for flexible printed circuit board markets. Phosphorus containing materials have been the focus for these halogen-free flame retardant composition, however phosphorus “bleed” and poor flexibility have been two of the many problems identified. A need therefore exists to address such shortcomings.